Bottom Line:
The effect of age, gender, and refractive error on NFD was analysed.We found a significant effect of age (center of the nerve-head (P = 0.006) and rim of the nerve head (P = 0.003)) and refractive error (center of nerve-head (P<0.001) and rim of nerve head (P<0.001)) on NFD.Age and refractive error have an effect on NFD.

Affiliation: Department of Ophthalmology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands. m.a.j.van.de.put@umcg.nl

ABSTRACT

Purpose: To measure the nerve-head to fovea distance (NFD) on fundus photographs in fellow eyes, and to compare the NFD between fellow eyes.

Methods: Diabetic patients without retinopathy, (n = 183) who were screened by fundus photography at the University Medical Center Groningen, the Netherlands from January 1(st) 2005 until January 1(st) 2006 were included. The NFD was measured in left and right eyes both from the center and from the rim of the nerve-head. To determine inter- and intra-observer agreement, repeated measurements by one observer (n = 3) were performed on all photographs and by two observers on 60 photographs (30 paired eyes). The effect of age, gender, and refractive error on NFD was analysed.

Results: The correlation of NFDs between the left and the right eye was 0.958 when measured from the center of the nerve head (mean difference 0.0078 mm. ±SD 0.079 (95% limits of agreement -0.147-0.163)) and 0.963 when measured from the rim (mean difference 0.0056±SD 0.073 (95% limits of agreement -0.137-0.149)). Using the NFD between fellow eyes interchangeably, resulted in a standard error of 0.153 mm. Intra- and inter-observer variability was small. We found a significant effect of age (center of the nerve-head (P = 0.006) and rim of the nerve head (P = 0.003)) and refractive error (center of nerve-head (P<0.001) and rim of nerve head (P<0.001)) on NFD.

Conclusions: The NFD in one eye provides a confident, reproducible, and valid method to address the position of the fovea in the fellow eye. We recommend using the NFD measured from the center of the nerve-head since the standard error by this method was smallest. Age and refractive error have an effect on NFD.

pone-0062518-g003: A. NFD measured from the center of the nerve-head of the right eye (OD) plotted against this measurement of the left eye (OS) together with the line of equation (N = 183).B. The distribution of differences between the NFDs measured in fellow eyes from the center of the nerve-head (N = 183). C. The difference between NFDs against NFD averaged over both eyes measured from the center of the nerve-head between fellow eyes. The solid line indicates the mean and the dotted lines the 95% limits of agreement (N = 183).

Mentions:
Figure 3 shows the diagnostic plots of agreement of NFDs measured in fellow eyes from the center of the nerve-head. Nine measurements (4.9%) made from the center of the nerve-head, and 12 measurements (6.6%) made from the rim of the nerve-head, were outside the 95% limits of agreement and no relationships between the mean and the difference were observed indicating that the measurement errors are normally distributed as required. The correlation of NFDs between fellow eyes was 0.958 when measured from the center of the nerve head and 0.963 when measured from the rim (Table 2). The average differences in NFD and the corresponding 95% limits of agreement in case of three repeated measurements are given in Table 2. These limits fall within the lateral resolution of our ultrasonography-instrument which is 0.2 mm, and hence the measurements of NFD are interchangeable between left and right eyes. When NFD would have been measured only once, the upper limit of the confidence interval for the upper limit of agreement for NFD measured from the center of the nerve head ( = 0.195 mm) is smaller than 0.2, which implies that the error in this measurement is still acceptable.

pone-0062518-g003: A. NFD measured from the center of the nerve-head of the right eye (OD) plotted against this measurement of the left eye (OS) together with the line of equation (N = 183).B. The distribution of differences between the NFDs measured in fellow eyes from the center of the nerve-head (N = 183). C. The difference between NFDs against NFD averaged over both eyes measured from the center of the nerve-head between fellow eyes. The solid line indicates the mean and the dotted lines the 95% limits of agreement (N = 183).

Mentions:
Figure 3 shows the diagnostic plots of agreement of NFDs measured in fellow eyes from the center of the nerve-head. Nine measurements (4.9%) made from the center of the nerve-head, and 12 measurements (6.6%) made from the rim of the nerve-head, were outside the 95% limits of agreement and no relationships between the mean and the difference were observed indicating that the measurement errors are normally distributed as required. The correlation of NFDs between fellow eyes was 0.958 when measured from the center of the nerve head and 0.963 when measured from the rim (Table 2). The average differences in NFD and the corresponding 95% limits of agreement in case of three repeated measurements are given in Table 2. These limits fall within the lateral resolution of our ultrasonography-instrument which is 0.2 mm, and hence the measurements of NFD are interchangeable between left and right eyes. When NFD would have been measured only once, the upper limit of the confidence interval for the upper limit of agreement for NFD measured from the center of the nerve head ( = 0.195 mm) is smaller than 0.2, which implies that the error in this measurement is still acceptable.

Bottom Line:
The effect of age, gender, and refractive error on NFD was analysed.We found a significant effect of age (center of the nerve-head (P = 0.006) and rim of the nerve head (P = 0.003)) and refractive error (center of nerve-head (P<0.001) and rim of nerve head (P<0.001)) on NFD.Age and refractive error have an effect on NFD.

Affiliation:
Department of Ophthalmology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands. m.a.j.van.de.put@umcg.nl

ABSTRACT

Purpose: To measure the nerve-head to fovea distance (NFD) on fundus photographs in fellow eyes, and to compare the NFD between fellow eyes.

Methods: Diabetic patients without retinopathy, (n = 183) who were screened by fundus photography at the University Medical Center Groningen, the Netherlands from January 1(st) 2005 until January 1(st) 2006 were included. The NFD was measured in left and right eyes both from the center and from the rim of the nerve-head. To determine inter- and intra-observer agreement, repeated measurements by one observer (n = 3) were performed on all photographs and by two observers on 60 photographs (30 paired eyes). The effect of age, gender, and refractive error on NFD was analysed.

Results: The correlation of NFDs between the left and the right eye was 0.958 when measured from the center of the nerve head (mean difference 0.0078 mm. ±SD 0.079 (95% limits of agreement -0.147-0.163)) and 0.963 when measured from the rim (mean difference 0.0056±SD 0.073 (95% limits of agreement -0.137-0.149)). Using the NFD between fellow eyes interchangeably, resulted in a standard error of 0.153 mm. Intra- and inter-observer variability was small. We found a significant effect of age (center of the nerve-head (P = 0.006) and rim of the nerve head (P = 0.003)) and refractive error (center of nerve-head (P<0.001) and rim of nerve head (P<0.001)) on NFD.

Conclusions: The NFD in one eye provides a confident, reproducible, and valid method to address the position of the fovea in the fellow eye. We recommend using the NFD measured from the center of the nerve-head since the standard error by this method was smallest. Age and refractive error have an effect on NFD.